The present invention relates to a novel coating method and an apparatus for applying a coating solution on an article to be coated and forming a water repellent film thereon.
A number of coating methods to form a film on an article to be coated are known in the prior art. There are, for example, the dipping process and the roll coating process.
The dipping process involves dipping the article in a coating solution and then pulling it up. This dipping process is not economical, because it requires the dipping solution in a quantity large enough to submerge the whole article. For dipping a large article, a large amount of coating solution has to be prepared. Another drawback to the dipping process is that a large vessel for the coating solution is required for coating a large article, which makes the coating equipment voluminous. Still another problem with the dipping process is that it is difficult to limit the part to be coated to a specific part of the article since the whole article will be coated.
For this reason, the roll coating process is used especially when the coating solution is applied to an article with a large area or to a specific part of the article.
In the conventional roll coating process, the coating solution is first loaded on a cylindrical roll and then, the article is brought into contact with the roll to transfer the coating solution thereon.
The problem with the roll coating process is that the curved surface of the roll often fails to fit on a curved surface of the article to be coated and to transfer the coating solution, because the coating is effected by bringing the roll into contact with the article. To overcome this problem, the roll may be made of a flexible or elastic material so as to fit on the curved surface of the article. But the contact pressure between the roll and the article is different from area to area, and a uniform coating can hardly be achieved. In addition, since the coating roll is usually installed horizontally, the way of moving the article in the coating operation is limited.